This invention relates to a device for detecting air bubbles in an intravenous solution being administered to a patient. The device is typically used as a safety feature in electrically driven precision pumps which pump precisely measured amounts of intravenous solution into the patient's bloodstream. This solution is typically conveyed through a transparent disposable plastic conduit which has a generally circular cross section. The solution involved may be of several types: a clear liquid such as the conventional dextrose solution used for intravenous feeding; an opaque milky liquid such as Intralipid.RTM.; or blood.
Methods for detecting air bubbles in such solutions by photoelectric means are well-known. They generally rely on a difference in the amount of light transmitted through the liquid and through air. Devices of this type, however, are inherently unsuitable for indiscriminate use with various kinds of intravenously administered solutions without appropriate adjustment.
To overcome this problem, devices have been marketed in which the light beam of the photoelectric bubble detector is directed not through the axis of the conduit, but through the wall of the conduit generally tangentially to its inner diameter. The difference in the reflective characteristics of the inner wall of the tube when liquid is present as opposed to the absence of liquid is detected by a light sensor and used to produce an appropriate signal indicating the presence of air. Unfortunately, the last-named method requires the use of a conduit whose translucence and dimensions must be controlled within tolerances so strict as to be economically undesirable for disposable equipment. In addition, the need for maintaining close tolerances in equipment of this type increases the chances of malfunction due to careless positioning of the conduit by the operator.